A principal objective of advance well completion is to have flow control over different inflow areas along the horizontal section of the well bore. This flow control is heavily dependent on the reliability of the open-hole packers that are installed to form isolated compartments defined by the production tubing and the surrounding reservoir rock wall that is the well bore. The purpose of installing the open-hole packers is to isolate the section of the production tubing that is perforated to receive the inflow of produced oil from the intervening spaces through which the remainder of the “blank” or imperforated tubing passes. As used herein, the term blank tubing means production tubing that is not perforated and does not constitute an inflow control device (ICD) for admitting hydrocarbon fluids into the tubing for production to the earth's surface.
The surface of the rock in the well bore can be irregular, even in carbonate formations. Such irregularities can interfere with the ability to form a reliable fluid-tight seal using the open-hole packer. At present, there is no method for confirming at the surface that the open-hole packers are completely sealing off the compartments as intended and that the objectives of the advance well completion have been achieved. What is required is a method for directly measuring the reliability of the open-hole packers to create the compartments in advance well completions. This determination is particularly important from the standpoint of well management, and because of the high cost of installing the open-hole packers.
The use of various types of tracers and tracer compositions in conjunction with well completions is known in the art. Several of the patents discussed below utilize tracers to identify the source of fluids produced from the reservoir and to identify specific locations or zones along the bore hole where the fluid(s) entered the bore hole.
One limited solution to the problem of identifying the general area that is the source of produced water has been to coat the interior of at least a portion of the pipe in the toe section of the horizontal tubing with a water-soluble phosphorescent composition. Water entering that compartment will solubilize the tracer. If tests of water produced with the oil at the surface show presence of the tracer compound, it will be known that at least the toe compartment was producing water. In the event of a failure of the packer adjacent the ICD, water containing the tracer will infiltrate the producing compartment and be produced with oil at the surface. Thus, the surface test will be inconclusive as to the actual location(s) of the water incursion(s).
The use of one or more tracer compositions applied to adjacent sections of tubing in a well completion is known. In U.S. Pat. No. 5,892,147, a method of dividing production tubing passing through a casing into a number of zones by packers positioned in the casing, and deploying a readily distinguishable tracer composition by means of explosive charges detonated in conjunction with a perforator gun is described. The amount and type of tracer composition detected with the produced oil and/or gas is utilized to estimate the flow rate through perforations in the various segregated zones.
A method for monitoring hydrocarbon and water production from different production zones/sections in a reservoir and/or injection wells is disclosed in U.S. Pat. No. 6,645,769. The method is said to be useful for differentiating between production of formation and/or injection water from various zones/sections and specifically for use in a “local alarm system” for water breakthrough. So-called “intelligent tracers” are used to distinguish between produced injection water and formation water from each zone/section. A specific tracer or tracers can be immobilized or placed on, e.g., a casing. The occurrence of a water breakthrough can be detected if the formation or a plug located in the formation releases a detectable tracer when the water or brine passes over the tracer composition and the released component is detected downstream. The principal focus of the patent is the disclosure of a wide variety of chemical, biological, radioactive and other types of tracer compositions and compounds, along with their respective detection methods. There is no specific teaching of a method in which a tracer can be used to indicate a failure of an open-hole packer to form or maintain a fluid-tight compartment adjacent the producing end of the tubing.
A method of determining the presence of undesired passageways that have been formed longitudinally between the bore hole wall and the inside peripheral wall of a casing are described in U.S. Pat. No. 3,848,124. One example of an undesirable passageway can be due to defects in a previous cementing job. Radioisotopes are placed adjacent to the casing at spaced-apart locations within the bore hole and on opposite sides of the production formation. The method appears to be limited to a bore hole in which the casing has been cemented in position by filling the annular space. The detection method seems to be limited to a gamma ray survey by logging the completed well.
The use of gravel packs containing distinctive tracers are described in U.S. Pat. No. 4,008,763 and U.S. Pat. No. 5,392,850. In the '763 patent, the use of one or more gravel packs is intended to prevent the infiltration of solids into the production stream and the presence of a tracer at the surface can be analyzed to determine which pack is leaking and requires reworking. The '850 patent includes the addition of a sub that can be actuated based upon tracer samples analyzed at the surface to release a permeability-reducing material into a gravel pack to restore its original functioning.
It will be understood that the pressures and temperatures to which the open-hole packers are subjected are substantial and that, as previously noted, the surrounding reservoir rock wall of the well bore can be irregular, even when drilled through carbonate formations.
It is therefore an object of the present invention to provide a reliable and inexpensive method and apparatus for determining whether water produced at the surface with the hydrocarbon fluid entered the ICD at the completion end, or other intermediate ICD location, from one or more adjacent compartments due to the failure of the open-hole packer(s) used to form the compartment(s).